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Plastic | Plastic Moulding and its Types

Plastic moulding.

Plastic moulding is the process of shaping plastic using a rigid frame or mould, the techniques allow for the creation of objects of all shapes and sizes with huge design flexibility for both simple and highly complex designs. Plastic moulding is the process of manufacturing by shaping liquid or pliable raw material using a rigid frame called a mould,

Types of Moulding Processes includes: -

A) Blow moulding-

Blow molding is a manufacturing process by which hollow plastic parts are formed. In general, there are three main types of blow moulding: Extrusion blow moulding, Injection blow moulding, and Injection stretch blow moulding. The blow moulding process begins with melting down the plastic and forming it into a parison or in the case of injection and injection stretch blow moulding (ISB) a preform. The parison is a tube-like piece of plastic with a hole in one end through which compressed air can pass.

Extrusion Blow Moulding

Extrusion Blow Moulding plastic is melted and extruded into a parison. This parison is then captured by closing it into a cooled metal mould. Air is then blown into the parison, inflating it into the shape of the hollow bottle, container, or
Part. After the plastic has cooled sufficiently, the mould is opened and the part is ejected. Continuous and Intermittent are two variations of Extrusion Blow Moulding.

Injection Blows Moulding (IBM)

Injection blows moulding is used for the production of hollow glass and plastic objects in large quantities. In the IBM process, the polymer is injection moulded onto a core pin; then the core pin is rotated to a blow molding station to be inflated and cooled. This is the least-used of the three blow molding processes, and is typically used to make small medical and single serve bottles. The process is divided into three steps: Injection, Blowing and Ejection.

Injection Stretch Blow Moulding

Injection Stretch Blow Moulding process, the plastic is first moulded into a "preform" using the injection molding process. These preforms are produced with the necks of the bottles, including threads on one end. These preforms are packaged, and fed later into a reheat stretch blow molding machine. In the ISB process, the preforms are heated above their glass transition temperature, then blown using high-pressure air into bottles using metal blow molds. The preform is always stretched with a core rod as part of the process.

B. Compression Moulding-

Compression moulding is a method of moulding in which the moulding material, generally preheated, is first placed in an open, heated mould cavity. The mould is closed with a top force or plug member, pressure is applied to force the material into contact with all mould areas, while heat and pressure are maintained until the moulding material has cured. The process employs thermosetting resins in a partially cured stage, either in the form of granules, putty-like masses, or preforms.

C. Extrusion Moulding-

Extrusion is a manufacturing process used to make pipes, hoses, drinking straws, curtain tracks, rods, and fiber. The granules melt into a liquid which is forced through a die, forming a long 'tube like' shape. The shape of the die determines the shape of the tube. The extrusion is then cooled and forms a solid shape. The tube may be printed upon, and cut at equal intervals. The pieces may be rolled for storage or packed together. Shapes that can result from extrusion include T-sections, U-sections, square sections, I-sections, L-sections and circular sections. One of the most famous products of extrusion moulding is the optical fibers cable.

D. Injection Moulding-

Injection moulding is a process which is basically used for mass production of plastic products, in this process the plastic granules are used as raw materials which are screwed towards the mould due to heavy friction they get heated and turns into liquid which is then injected into the metallic mould and as the plastic solidifies the final product is taken out by injection pins through the movable mould.

E. Laminating-

Lamination is the technique of manufacturing a material in multiple layers, so that the composite material achieves improved strength, stability, sound insulation, appearance or other properties from the use of differing materials. A laminate is a permanently assembled object by heat, pressure, welding, or adhesives.

F. Matrix Moulding-

Matrix moulding or matrix transfer moulding is a technique often used during moulding. The person doing the assembly will first create the rigid outer shell, then introduce the softer and more fluid moulding material between the shell and the prototype. This process is often used for complex shapes using composites such as with glass and glass/ceramic composites.

G. Rotational moulding- 

Rotational Molding is also called rotocasting, it involves a heated hollow mold which is filled with a charge or shot weight of material. It is then slowly rotated in three different directions causing the softened material to disperse and stick to the walls of the mold. In order to maintain uniform thickness throughout the part, the mold continues to rotate at all times during the heating phase and to avoid sagging or deformation also during the cooling phase.
H. Spin casting- Spin casting, also known as centrifugal rubber mold casting (CRMC), is a method of utilizing centrifugal force to produce castings from a rubber mold. Typically, a disc-shaped mold is spun along its central axis at a set speed.

I. Transfer Molding-

Transfer molding is a process where the amount of material is measured and inserted before the molding process takes place. The material is then preheated and loaded into a pot and a plunger is then used to force the material from the pot through the runner system into the mold cavities.

J. Thermoforming-

Thermoforming is a manufacturing process where a plastic sheet is heated to a pliable forming temperature, formed to a specific shape in a mold, and trimmed to create a usable product. The sheet, or "film" when referring to thinner gauges and certain material types, is heated in an oven to a high-enough temperature that permits it to be stretched into or onto a mold and cooled to a finished shape. Its simplified version is vacuum forming.

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